The present disclosure relates generally to semiconductor device manufacturing and, more particularly, to bond gap control structures (BGCS) for wafer level packaged optical microelectromechanical systems (MEMS) devices.
Microelectromechanical systems (MEMS) are integrated micro devices or systems combining electrical and mechanical components. MEMS devices may be fabricated using, for example, standard integrated circuit batch processing techniques. Exemplary applications for MEMS devices include sensing, controlling, and actuating on the micro scale. Such MEMS devices may function individually or in arrays to generate effects on a macro scale.
Many MEMS devices require a vacuum environment in order to attain maximum performance. The vacuum package also provides protection and an optimal operating environment for the MEMS device. Specific examples of these MEMS devices include infrared MEMS such as bolometers, and certain inertial MEMS such as gyros and accelerometers. Previously, MEMS devices have been individually packaged in vacuum compatible packages after fabrication and dicing of the MEMS device. Often, however, the cost of packaging MEMS devices in traditional metal or ceramic packages may be on the order of about 10 to 100 times the device fabrication cost. This especially true if a vacuum is required in the package. These high packaging costs therefore make it difficult to develop commercially viable vacuum packaged MEMS devices. In addition, MEMS devices are fragile especially after dicing. Care must be taken in handling these devices, and traditional integrated circuit fabrication machinery cannot adequately handle and protect MEMS devices. Thus, special handling techniques have also been developed to protect the MEMS devices until vacuum packaging has been completed. These special handling procedures also add additional cost to the production of MEMS devices.
Wafer Level Packaging (WLP) was developed to address the high cost of packaging of MEMS by eliminating the traditional packages. In the WLP process, two semiconductor wafers may be bonded together using a joining material to yield bonded wafers. For example, a device wafer may be bonded to a lid wafer using an adhesive or solder to form a packaged MEMS device. Certain applications may require that the joining material form a substantially uniform bond line. In certain situations, substrates (such as silicon wafers) may be bonded together using a joining material. After bonding, the joining material forms a bond line in between the substrates. However, the uniformity of the bond line may be affected by the flatness of the substrates and the uniformity of the bond force used to bond the wafers. The uniformity of the bond line may be controlled by placing spacers at certain intervals across the surface of one or both substrates. However, adding the spacers usually requires adding process steps to the fabrication process.